How do organisms perceive moving objects, specifically their direction and velocity of movement? We plan to study this by analyzing the mechanism of directional selectivity of single neurons in visual cortex of cat (Area 17). By examining the microelectrode recording techniques, the response of such neurons to light and dark moving edges, moving at various velocities, as well as their response to single flashes of light, we hope to narrow the range of possible neurophysiological mechanisms (i.e., models) mediating movement perception. We also hope to provide some quantitative understanding of the visual system's response to diverse velocities of motion.